Technical Field
The present disclosure relates generally to the field of combustion melters and apparatus, and methods of use, and more specifically to submerged and conventional combustion melters, and methods of their use, particularly for melting glass-forming materials, mineral wool forming materials, and other non-metallic inorganic materials.
Background Art
A submerged combustion melter (SCM) may be employed to melt glass batch and/or waste glass materials to produce molten glass, or may melt mineral wool feedstock to make mineral or rock wool, by passing oxygen, oxygen-enriched mixtures, or air along with a liquid, gaseous and/or particulate fuel (some of which may be in one or more of the feedstock materials), directly into a molten pool of glass or other material, usually through burners submerged in a turbulent melt pool. The introduction of high flow rates of products of combustion of the oxidant and fuel into the molten material, and the expansion of the gases during submerged combustion (SC), cause rapid melting of the feedstock and much turbulence and foaming. Conventional melters operate primarily by combusting fuel and oxidant above the molten pol of melt, and are very laminar in flow characteristics compared to SCMs. While most of the present disclosure discusses SCM, the disclosure is pertinent to conventional melters as well.
Oxy-fuel burners and technologies provide high heat transfer rates, fuel consumption reductions (energy savings), reduced volume of flue gas, and reduction of pollutants emission, such as oxides of nitrogen (NOx), carbon monoxide (CO), and particulates. Despite the reduction of the flue gas volume that the substitution of combustion with air by combustion with pure oxygen or oxygen-enriched air yields, a significant amount of energy is lost in the flue gas (also referred to herein as exhaust or exhaust gases), especially for high temperature processes. For example, in an oxy-fuel fired glass furnace where all the fuel is combusted with pure oxygen, and for which the temperature of the flue gas at the furnace exhaust is of the order of 1350° C., typically 30% to 40% of the energy released by the combustion of the fuel is lost in the flue gas. It would be advantageous to recover some of the energy available from the flue gas in order to improve the economics of operating an oxy-fuel fired furnace, whether SCM or conventional melter.
One technique consists in using the energy available in the flue gas to preheat and/or dry out the raw materials before loading them into the furnace. In the case of glass melting, the raw materials may comprise recycled glass, commonly referred to as Gullet, and other minerals and chemicals in a pulverized form referred to as batch materials that have a relatively high water content. The energy exchange between the flue gas and the raw materials may be carried out in a batch/cullet preheater. Such devices are commonly available, for example from Zippe Inc. of Wertheim, Germany. Experience shows that this technology is difficult to operate when the batch represents more than 50% of the raw materials because of a tendency to plug. This limits the applicability of the technique to a limited number of glass melting operations that use a large fraction of cullet. Another drawback of this technique (according to the known art) is that the inlet temperature of the flue gas in the materials preheater must be generally kept lower than 600° C. in the case of an oxy-fuel fired furnace where the flue gas is produced at a temperature higher than 1000° C., one reference (U.S. Pat. No. 6,250,916) discloses that cooling of the flue gas prior to the materials preheater would be required. This would be counterproductive.
One low-cost non-metallic inorganic material being used to make inorganic fibers is basalt rock, sometimes referred to as lava rock. US20120104306 discloses a method for manufacturing basalt filament, comprising the steps of grinding basalt rock as a material, washing a resultant ground rock, melting the ground rock that has been washed, transforming a molten product into fiber, and drawing the fiber in an aligned manner, and winding it. The temperature of the molten product in the melting step is 1400 to 1650° C., and log η is 2.15 to 2.35 dPa·s and more preferably 2.2 to 2.3 dPa·s, where η is the viscosity of the molten product. The size of basalt rock may be on the order of several mm to several dozens of mm, or several μm to several dozens of mm, according to this reference.
It would be an advanced in the melter art, and in particular the submerged combustion melter art, to improve energy usage while avoiding the heat loss from the exhaust while melting granular or pellets-size material (much larger than several dozens of mm), and prolong the run-length or campaign length of submerged combustion melters.